How can I fix stair lift?

How can I get a Stannah Model 300 straight stairlift working again?All the fuses and electrics have been checked and the safety pads are ok.The chair is at the bottom of the stair but when the button is engaged to take the chair up there is a click but the chair will not move.When manually moving the chair up with the handwinding handle the chair moves and will return to the original position using the button but will not move up the track when using any of the up buttons!Any suggestions gratefully received...